Make back-channel logout work on existing sessions

crates/storage-pg/migrations/20250709142230_backfill_id_token_claims.sql

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+-- Copyright 2025 New Vector Ltd.
+--
+-- SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+-- Please see LICENSE in the repository root for full details.
+
+-- We may be running an older version of the app that doesn't fill in the
+-- id_token_claims column when the id_token column is populated. So we add a
+-- trigger to fill in the id_token_claims column if it's NULL.
+--
+-- We will be able to remove this trigger in a future version of the app.
+--
+-- We do this before the backfilling starts, to make sure we don't miss anything
+CREATE OR REPLACE FUNCTION fill_id_token_claims()
+RETURNS TRIGGER AS $$
+BEGIN
+    -- Only process if id_token_claims is NULL but id_token is not NULL
+    IF NEW.id_token_claims IS NULL AND NEW.id_token IS NOT NULL AND NEW.id_token != '' THEN
+        BEGIN
+            -- Decode JWT payload inline
+            NEW.id_token_claims := (
+                CASE
+                    WHEN split_part(NEW.id_token, '.', 2) = '' THEN NULL
+                    ELSE
+                        (convert_from(
+                            decode(
+                                replace(replace(split_part(NEW.id_token, '.', 2), '-', '+'), '_', '/') ||
+                                repeat('=', (4 - length(split_part(NEW.id_token, '.', 2)) % 4) % 4),
+                                'base64'
+                            ),
+                            'UTF8'
+                        ))::JSONB
+                END
+            );
+        EXCEPTION
+            WHEN OTHERS THEN
+                -- If JWT decoding fails, leave id_token_claims as NULL
+                NEW.id_token_claims := NULL;
+        END;
+    END IF;
+
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Create the trigger
+CREATE TRIGGER trg_fill_id_token_claims
+    BEFORE INSERT OR UPDATE ON upstream_oauth_authorization_sessions
+    FOR EACH ROW
+    EXECUTE FUNCTION fill_id_token_claims();
+
+-- This backfills the id_token_claims column in the upstream_oauth_authorization_sessions table
+-- by decoding the id_token column and storing the decoded claims in the id_token_claims column.
+UPDATE upstream_oauth_authorization_sessions
+SET id_token_claims = CASE
+    WHEN id_token IS NULL OR id_token = '' THEN NULL
+    WHEN split_part(id_token, '.', 2) = '' THEN NULL
+    ELSE
+        (convert_from(
+            decode(
+                replace(replace(split_part(id_token, '.', 2), '-', '+'), '_', '/') ||
+                repeat('=', (4 - length(split_part(id_token, '.', 2)) % 4) % 4),
+                'base64'
+            ),
+            'UTF8'
+        ))::JSONB
+END
+WHERE id_token IS NOT NULL AND id_token_claims IS NULL;